An article having a component with a concave surface or a convex surface or an article having a number of concave surfaces or convex surfaces arranged thereon can be used in various industrial fields. In some applications, the concave or convex surface can function as a lens. For example, a sheet-like article having a number of concave surfaces or convex surfaces arranged thereon can function as an array of lenses such as an array of microlenses (i.e., microlens array). Such a sheet-like article that can be used as a microlens array has recently received a great amount of attention. Microlens array may be suitable for various optical applications including, for example, a display, a semiconductor laser, and an optical fiber.
Japanese Patent Application Laid-Open No. H11-142609 describes a manufacturing method for a microlens array using an indentation method. According to this manufacturing method, many indentations are formed on the surface of a mold using a pressing tool. The pressing tool, which has a spherical shaped head of different sizes, is repeatedly pressed on the surface of the mold at regular intervals. A microlens array can then be manufactured by compression molding an optical-grade plastic, such as an acrylic polymer, using the mold having the indentations formed thereon. However, the manufacturing method of a microlens array using this indentation method requires considerable time and cost because of the amount of work needed to form the mold with many indentations.
Japanese Patent Application Laid-Open No. H05-134103 describes a manufacturing method for a microlens array using an electron-beam lithographic method. In this manufacturing method, many microlenses can be formed on a base sheet using an electron beam. Like the indentation method for manufacturing a microlens array, this method requires considerable time and cost. It could take greater than ten days to several hundred days to manufacture more than ten thousand to several hundred thousand microlenses with each microlens having a diameter of about 100 micrometers (μm), for example.
Japanese Patent Application Laid-Open No. S62-260104 describes a manufacturing method for a microlens using a laser chemical vapor deposition (CVD) method. In this manufacturing method, a substrate is set in a container filled with a mixed gas composition, a laser beam is irradiated on the substrate to decompose the gas composition, and a lens material is deposited on the substrate to form the microlens. The desired shape can be obtained by changing the energy distribution of the laser beam to vary the amount of material deposited on the substrate. However, because each microlens is formed individually by finely changing the energy distribution of the laser beam, this manufacturing method is slow and costly.
Japanese Patent Application Laid-Open No. H05-134103 describes a manufacturing method for a microlens array that includes preparing a lattice frame, placing a resin within the lattice frame, and melting the resin to form curved surfaces suitable for microlenses by means of the surface tension of the melted resin. Although an article having a convex surface can be manufactured relatively easily with this manufacturing method in comparison with the aforementioned electron-beam lithographic method and laser chemical vapor deposition method, it is necessary to prepare the lattice frame using a photoresist prior to forming microlenses. The method of preparing the lattice frame can be complicated. Therefore, the overall steps of manufacturing a microlens array using this method can be time consuming and costly. Further, because this manufacturing method includes the step of melting the photo-resist or resin material, the range of suitable materials that can be used is limited. It can be difficult to find materials that have suitable melting properties as well as suitable optical properties.
C. Y. Chang et al. reported a manufacturing method for a microlens array made of a resin material in Infrared Physics & Technology, 48, pp. 163-173 (2006). In this manufacturing method, a resin film is set on a mold disposed in a closed chamber and then heated. High gas pressures are used to extrude the resin film into dimples of the mold, thereby forming convex surfaces. The size and shape of the convex surfaces that can be formed are limited, however, because the hardened resin film must be reheated to form the microlenses. Additionally, since this method involves high-temperatures and high gas pressures, the manufacturing cost can be high.
Easier methods are desired for manufacturing an article having at least one concavity or at least one convexity on its surface. More particularly, easier methods are desired for manufacturing an article having at least one micro-concavity or at least one micro-convexity on its surface.